Biguanide derivative and therapeutic agent for diabetes containing the same

ABSTRACT

Diabetes treatments comprising, as effective ingredients, biguanide derivatives represented by the following general formula (1), or salts thereof.  
                 
 
(wherein R 1 , R 2  and R 3  may be the same or different and each represents one selected from the group consisting of hydrogen, optionally substituted lower alkyl groups and optionally substituted lower alkylthio groups).

TECHNICAL FIELD

The present invention relates to biguanide derivatives and saltsthereof, and to therapeutic agents for the treatment of diabetescomprising the same.

BACKGROUND ART

Treatments for type II (non-insulin dependent) diabetes are currentlycentered on hypoglycemic agents. Strict blood glucose control clearlylowers rates of transition to complications and mortality rates. Themajor hypoglycemic agents used are insulin preparations or oralhypoglycemic agents such as sulfonylurea agents, thiazolidinederivatives, α-glucosidase inhibitors, biguanide agents and the like.Among such oral hypoglycemic agents, biguanide agents are known to bethe most effective in type II diabetic patients. Numerous biguanidederivatives have been synthesized to date, and the hypoglycemic actionsof various biguanide derivatives have been reported in publications suchas, for example, J. Am. Chem. Soc., 81, 3728-3736 (1959). However, suchbiguanide derivatives are commonly recognized as having the potential toinduce lactic acidosis, and even the aforementioned publications havenot confirmed the presence or degree of blood lactic acid levelaugmenting effects of biguanide derivatives. Consequently, the existingbiguanide agents, such as metformin, have been contraindicated fordiabetic patients with anamnesis of lactic acidosis, diabetic patientswith kidney dysfunction, diabetic patients with liver dysfunction,diabetic patients with cardiovascular dysfunction, diabetic patientswith pulmonary dysfunction, diabetic patients susceptible to hypoxia,diabetic patients consuming excessive alcohol, diabetic patients withgastrointestinal disturbance and elderly diabetic patients, due to therisk of their causing lactic acidosis (DRUGS in JAPAN : Ethical Drugs,23rd edition, p.2094, 2000, Japan Pharmaceutical Information Center).

In addition, approximately 10% of type II diabetic patients are said tohave overt nephropathy, therefore many patients cannot take biguanideagents. Sulfonylurea agents, thiazolidine derivatives and insulinpreparations are administered in such cases, but because these agentsproduce a hunger craving and thus tend to result in increased bodyweight, such agents cannot be considered suitable for obese diabeticpatients. A demand therefore exists for biguanide agents which lowerblood glucose substantially without increasing blood lactic acid levels,in order to reduce the risk of inducing lactic acidosis.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished in light of theaforementioned problems of the prior art, and its object is to provide adiabetes treatment which adequately suppresses elevation in bloodglucose levels and even satisfactorily lowers blood glucose levelswhile, preferably, also exhibiting an effect of sufficiently suppressingelevation in blood lactic acid levels, and which can therefore beadministered to diabetic patients with kidney dysfunction who aresusceptible to lactic acidosis.

As a result of much diligent research directed toward achieving theobject, the present inventors found that novel biguanide derivativeshaving a specific structure exhibit an excellent hypoglycemic effect,and the present invention was completed based on this finding.

Specifically, the present invention provides a biguanide derivativerepresented by the following general formula (1) or a salt thereof:

(wherein R¹, R² and R³ may be the same or different and each representsone selected from the group consisting of hydrogen, an optionallysubstituted lower alkyl group and an optionally substituted loweralkylthio group).

The invention also provides a therapeutic agent for the treatment ofdiabetes, comprising as an active ingredient, the biguanide derivativerepresented by general formula (1) above or the salt thereof.

The therapeutic agent for the treatment of diabetes of the inventionhave excellent hypoglycemic effects (preferably effects of loweringblood glucose without substantial increase of blood lactic acid levels),and is therefore useful as a therapeutic agent for the treatment ofdiabetes for blood glucose elevation-suppressing therapy which do notinduce lactic acidosis. More specifically, it is useful as a therapeuticagent for the treatment of diabetes, wherein the target disease is atleast one disease selected from the group consisting of diabetes withanamnesis of lactic acidosis, diabetes with kidney dysfunction, diabeteswith liver dysfunction, diabetes with cardiovascular dysfunction,diabetes with pulmonary dysfunction, hypoxia-susceptible diabetes,diabetes with excessive alcohol consumption, diabetes withgastrointestinal disturbance and elderly diabetes, and particularly itis useful as a therapeutic agent for the treatment of diabetes targetedto diabetes with kidney dysfunction.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments for carrying out the invention will now beexplained in detail. First, the biguanide derivatives of the inventionand their salts will be explained.

The biguanide derivatives of the invention are compounds represented bythe following general formula

wherein R¹, R² and R³ may be the same or different and each representsone selected from the group consisting of hydrogen, an optionallysubstituted lower alkyl group and an optionally substituted loweralkylthio group.

As the lower alkyl groups there are preferred linear or branched alkylgroups of 1-6 carbons, and specifically there may be mentioned methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl,pentyl groups, hexyl groups and the like. Among these lower alkylgroups, those with 1-5 carbons are preferred, those with 1-4 carbons aremore preferred, and methyl is especially preferred.

As the lower alkylthio groups there are preferred linear or branchedalkylthio groups of 1-6 carbons, and specifically there may be mentionedmethylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio,isobutylthio, sec-butylthio, tert-butylthio, pentylthio groups,hexylthio groups and the like. Among these lower alkylthio groups, thosewith 1-5 carbons are preferred, those with 1-4 carbons are morepreferred, and methylthio is especially preferred.

As substituents for the lower alkyl groups and alkylthio groups theremay be mentioned lower alkylthio groups and lower alkoxy groups, amongwhich linear or branched alkylthio groups of 1-6 (more preferably 1-4)carbons are preferred, and methylthio is especially preferred.

As the novel biguanide derivatives according to the invention there maybe mentioned, specifically, 1-[(furan-3-yl)methyl]biguanide,1-[(2-methylfuran-3-yl)methyl]biguanide,1-[(4-methylfuran-3-yl)methyl]biguanide,1-[(5-methylfuran-3-yl)methyl]biguanide,1-[(2-ethylfuran-3-yl)methyl]biguanide,1-[(4-ethylfuran-3-yl)methylgbiguanide,1-[(5-ethylfuran-3-yl)methyl]biguanide,1-[(2-tert-butylfuran-3-yl)methyl]biguanide,1-[(4-tert-butylfuran-3-yl)methyl]biguanide,1-[(5-tert-butylfuran-3-yl)methyl]biguanide,1-[(2,4-dimethylfuran-3-yl)methyl]biguanide,1-[(2,5-dimethylfuran-3-yl)methyl]biguanide,1-[(4,5-dimethylfuran-3-yl)methyl]biguanide,1-[(2,4,5-trimethylfuran-3-yl)methyl]biguanide,1-[(2-methylthiomethylfuran-3-yl)methyl]biguanide,1-[(4-methylthiomethylfuran-3-yl)methyl]biguanide,1-[(5-methylthiomethylfuran-3-yl)methyl]biguanide, and the like.

The salts of biguanide derivatives represented by general formula (1)above may be in the form of pharmacologically acceptable salts, such as,for example, inorganic acid salts, organic acid salts, acidic amino acidsalts and the like. As examples of inorganic acid salts there may bementioned salts with hydrochloric acid, hydrobromic acid, nitric acid,sulfuric acid and phosphoric acid. As examples of organic acid saltsthere may be mentioned salts with formic acid, acetic acid,trifluoroacetic acid, fumaric acid, oxalic acid, tartaric acid, maleicacid, citric acid, succinic acid, malic acid, methanesulfonic acid,benzenesulfonic acid and p-toluenesulfonic acid. As examples of acidicamino acid salts there may be mentioned salts with aspartic acid andglutamic acid. Preferred among these salts of biguanide derivativesrepresented by general formula (1) are salts with inorganic acids, andespecially salts with hydrochloric acid.

The compounds represented by general formula (1) may be synthesizedusing the corresponding (furan-3-yl)methylamine or (substitutedfuran-3-yl)methylamine as starting materials. Commercially available(furan-3-yl)methylamine (manufactured by Maybridge Chemical, forexample) may be used. As a (substituted furan-3-yl)methylamine there maybe used one produced by the following reaction scheme. In this reactionscheme, R¹, R² and R³ have the same definitions as R¹, R² and R³ ingeneral formula (1) above.

A target (substituted furan-3-yl)methylamine may be obtained by reducingthe corresponding substituted furan-3-carboxamide (J. Med. Chem.,42(15), 2920-2926(1999)), substituted furan-3-carbonitrile (J.Heterocycl. Chem., 33(6), 2007-2011(1996)), (substitutedfuran-3-yl)methylazide or substituted furan-3-carbaldehyde oxime.Alternatively, it may be synthesized from a (substitutedfuran-3-yl)methylphthalimide (J. Med. Chem., 42(5), 2920-2926(1999)). Asubstituted furan-3-carboxamide may be synthesized from thecorresponding substituted furan-3-carboxylic acid ester. A (substitutedfuran-3-yl)methylazide and (substituted furan-3-yl)methylphthalimide maybe directly synthesized from a (substituted furan-3-yl)methyl alcohol byMitsunobu reaction, or they may be synthesized via an alkylsulfonatesuch-as mesyl or tosyl, or a halogenated compound such as chloro orbromo. A (substituted furan-3-yl)methyl alcohol may be synthesized byreduction of the corresponding substituted furan-3-carbaldehyde. Asubstituted furan-3-carbaldehyde oxime may be obtained by reaction ofthe corresponding substituted furan-3-carbaldehyde and hydroxylamine.

Cyanoguanidine may be mentioned as an additional starting material to beused for production of a compound represented by general formula (1),and it may be commercially available products (for example, by TokyoKasei, Kanto Chemicals, Wako Pure Chemical Industries or Aldrich).

The compounds represented by general formula (1) may be produced byreaction with cyanoguanidine in the presence of silylating agents,either in solvents that do not affect the (furan-3-yl)methylamine or(substituted furan-3-yl)methylamine reaction, or without solvents. Asexamples of such solvents there may be mentioned hexane, cyclohexane,benzene, toluene, diethyl ether, diisopropyl ether, tert-butylmethylether, tetrahydrofuran, dioxane, dichloromethane, 1,2-dichloroethane andchloroform, with dichloromethane, 1,2-dichloroethane, benzene andtoluene being preferred. These solvents may also be used in mixedsolvents of two or more.

The reaction temperature is not particularly restricted so long as it isa temperature from −78° C. to the boiling point of the reaction mixture,but it is preferably room temperature.

As examples of silylating agents there may be mentionedchlorotrimethylsilane (Me₃SiCl (Me₃Si will hereinafter be abbreviated asTMS)), chlorotriethylsilane (Et₃SiCl), trimethylsilyltrifluoromethanesulfonate (TMSOSO₂CF₃), trimethylsilyl methanesulfonate(TMSOSO₂CH₃), (TMSO)₂SO₂, t-BuMe₂SiOSO₂CF₃, (TMSO)(TMSN)CMe, among whichtrimethylsilyl trifluoromethanesulfonate and trimethylsilylmethanesulfonate are preferred.

A scheme for the production method for the compounds represented bygeneral formula (1) is shown below. The symbols R¹, R² and R³ in thescheme have the same definition as R¹, R² and R³ in general formula (1)above.

Next, the therapeutic agent for the treatment of diabetes of theinvention will be explained. The therapeutic agent for the treatment ofdiabetes of the invention comprises as an active ingredient thebiguanide derivative represented by the general formula (1) or the saltthereof. There are no particular restrictions on the specificformulations of the therapeutic agent for the treatment of diabetes ofthe invention, so long as it comprises the above-mentioned biguanidederivatives or the salts thereof as an active ingredient, and forexample, they may be in admixture with additives such as excipients,binders, stabilizers, lubricants, taste correctors, disintegrants,coating agents, coloring agents, buffering agents, aqueous solvents,oily solvents, isotonizing agents, dispersing agents, preservatives,solubilizing agents, fluidizing agents, soothing agents, pH adjustors,antiseptics, bases and the like. Physiologically acceptable carriers mayalso be used as additives in the therapeutic agent for the treatment ofdiabetes.

As examples of excipients there may be mentioned sugars such as lactose,saccharose, glucose, D-mannitol and sorbit, cellulose and itsderivatives such as crystalline cellulose, hydroxypropyl cellulose,hydroxypropylmethyl cellulose and methyl cellulose, starches and theirderivatives such as corn starch, potato starch, α-starch, dextrin,β-cyclodextrin, carboxymethyl starch sodium and hydroxypropyl starch,silicates such as synthetic aluminum silicate, magnesiumaluminosilicate, calcium silicate and magnesium silicate, phosphatessuch as calcium phosphate, carbonates such as calcium carbonate,sulfates such as calcium sulfate, and tartaric acid, potassium hydrogentartrate, magnesium hydroxide and the like.

As examples of binders there may be mentioned cellulose and itsderivatives such as crystalline cellulose, hydroxypropyl cellulose,hydroxypropylmethyl cellulose and methyl cellulose, starches and theirderivatives such as corn starch, potato starch, α-starch, dextrin,β-cyclodextrin, carboxymethyl starch sodium and hydroxypropyl starch,sugars such as lactose, saccharose, glucose, D-mannitol and sorbit, andagar, stearyl alcohol, gelatin, tragacanth, polyvinyl alcohol, polyvinylpyrrolidone, and the like.

As examples of stabilizers there may be mentioned parahydroxybenzoicacid esters such as methyl paraben and propyl paraben, alcohols such aschlorobutanol, benzyl alcohol and phenylethyl alcohol, phenols such asphenol and cresol, sulfite salts such as sodium bisulfite and sodiumsulfite, edetic acid salts such as sodium edetate and tetrasodiumedetate, and hydrogenated oils, sesame oil, sodium chondroitin sulfate,dibutylhydroxytoluene, adipic acid, ascorbic acid, stearic L-ascorbateesters, sodium L-ascorbate, L-aspartic acid, sodium L-aspartate,acetyltryptophan sodium, acetanilide, aprotinin solution,aminoethylsulfonic acid, aminoacetic acid, DL-alanine, L-alanine,benzalkonium chloride, sorbic acid and the like.

As examples of lubricants there may be mentioned stearic acids such asstearic acid, calcium stearate and magnesium stearate, waxes such aswhite beeswax and carnauba wax, sulfates such as sodium sulfate, silicicacid compounds such as magnesium silicate and light silicic anhydride,lauryl sulfates such as sodium lauryl sulfate, and gum arabic powder,cacao butter, carmellose calcium, carmellose sodium, callopeptide,hydrated silicon dioxide, hydrated amorphous silicon oxide, dry aluminumhydroxide gel, glycerin, light liquid paraffin, crystalline cellulose,hydrogenated oil, synthetic aluminum silicate, sesame oil, wheat starch,talc, macrogols, phosphoric acid and the like.

As examples of taste correctors there may be mentioned sugars such aslactose, saccharose, glucose and D-mannitol, and ascorbic acid,L-aspartic acid, sodium L-aspartate, magnesium L-aspartate, aspartame,sweet hydrangea, sweet hydrangea extract, sweet hydrangea powder,aminoethylsulfonic acid, aminoacetic acid, DL-alanine, saccharin sodium,dl-menthol, 1-menthol and the like.

As examples of disintegrants there may be mentioned cellulose and itsderivatives such as crystalline cellulose, hydroxypropyl cellulose,hydroxypropylmethyl cellulose and methyl cellulose, carbonates such ascalcium carbonate, sodium bicarbonate and magnesium carbonate, starchesand their derivatives such as corn starch, potato starch, α-starch,dextrin, β-cyclodextrin, carboxymethyl starch sodium and hydroxypropylstarch, and gelatin, tragacanth, adipic acid, alginic acid, sodiumalginate and the like.

As examples of coating agents there may be mentioned cellulosederivatives such as cellulose acetate, hydroxypropyl cellulose,cellulose acetate phthalate and hydroxypropylmethyl cellulose, andshellac, polyvinyl pyrrolidones, polyethylene glycol, macrogols,methacrylic acid copolymers, liquid paraffin, eudragit, and the like.

As examples of coloring agents there may be mentioned indigo carmine,caramel, riboflavin and the like.

As examples of buffering agents there may be mentioned aminoacetic acid,L-arginine, benzoic acid, sodium benzoate, ammonium chloride, potassiumchloride, sodium chloride, dried sodium sulfite, dried sodium carbonate,diluted hydrochloric acid, citric acid, calcium citrate, sodium citrate,disodium citrate, calcium gluconate, L-glutamic acid, sodiumL-glutamate, creatihine, chlorobutanol, crystalline sodium dihydrogenphosphate, disodium succinate, acetic acid, potassium acetate, sodiumacetate, tartaric acid, sodium bicarbonate, sodium carbonate,triethanolamine, lactic acid, sodium lactate solution, glacial aceticacid, boric acid, maleic acid, citric anhydride, anhydrous sodiumcitrate, anhydrous sodium acetate, anhydrous sodium carbonate, anhydroussodium hydrogen phosphate, anhydrous trisodium phosphate, anhydroussodium dihydrogen phosphate, dl-malic acid, phosphoric acid, trisodiumphosphate, sodium hydrogen phosphate, dipotassium phosphate, potassiumdihydrogen phosphate, sodium dihydrogen phosphate, sodium dihydrogenphosphate hydrate and the like.

As examples of aqueous solvents there may be mentioned distilled water,physiological saline, Ringer's solution and the like.

As examples of oily solvents there may be mentioned vegetable oils suchas olive oil, sesame oil, cotton oil and corn oil, and propylene glycol,and the like.

As examples of isotonizing agents there may be mentioned potassiumchloride, sodium chloride, glycerin, sodium bromide, D-sorbitol,nicotinamide, glucose, boric acid and the like.

As examples of dispersing agents there may be mentioned stearic acid andits salts such as zinc stearate and magnesium stearate, and gum arabic,propyleneglycol alginate, sorbitan sesquioleate, D-sorbitol, tragacanth,methyl cellulose, aluminum monostearate, aminoalkyl methacrylatecopolymer RS, lactose, concentrated glycerin, propylene glycol,macrogols, sodium lauryl sulfate and the like.

As examples of preservatives there may be mentioned alcohols such aschlorobutanol, phenethyl alcohol, propylene glycol and benzyl alcohol,parahydroxybenzoic acid esters such as isobutyl parahydroxybenzoate,ethyl parahydroxybenzoate and methyl parahydroxybenzoate, andbenzalkonium chloride, benzethonium chloride, dried sodium sulfite,dried sodium sulfate, cresol, chlorocresol, dibutylhydroxytoluene,potassium sorbate, sodium dehydroacetate, phenol, formalin, phosphoricacid, benzoin, thimerosal, thymol, sodium dehydroacetate and the like.

As examples of solubilizing agents there may be mentioned sodiumbenzoate, ethylenediamine, citric acid, sodium citrate, glycerin, sodiumacetate, sodium salicylate, sorbitan sesquioleate, nicotinamide,glucose, benzyl alcohol, polyvinyl pyrrolidones, acetone, ethanol,isopropanol, D-sorbitol, sodium hydrogen carbonate, sodium carbonate,lactose, urea, saccharose and the like.

As examples of fluidizing agents there may be mentioned stearic acid andits salts such as calcium stearate and magnesium stearate, and hydratedsilicon dioxide, talc, absolute ethanol, crystalline cellulose,synthetic aluminum silicate, calcium hydrogen phosphate and the like.

As examples of soothing agents there may be mentioned benzalkoniumchloride, procaine hydrochloride, meprylcaine hydrochloride, lidocainehydrochloride, lidocaine and the like.

As examples of pH adjustors there may be mentioned hydrochloric acid,citric acid, succinic acid, acetic acid, boric acid, maleic acid, sodiumhydroxide and the like.

As examples of antiseptics there may be mentioned benzoic acid, sodiumbenzoate, cetylpyridinium chloride, salicylic acid, sodium salicylate,sorbic acid, potassium sorbate, thymol, methyl parahydroxybenzoate,butyl parahydroxybenzoate and the like.

As examples of bases there may be mentioned vegetable oils such as oliveoil, sesame oil and wheat germ oil, and glycerin, stearyl alcohol,polyethylene glycols, propylene glycol, cetanol, lard, white vaseline,paraffin, bentonite, isopropyl lanolin fatty acids, vaseline,polysorbates, macrogols, lauryl alcohol, sodium lauryl sulfate, ethyllinoleate, sodium hydrogen phosphate, rosins and the like.

The amount of the biguanide derivative represented by general formula(1) or the salt thereof in the therapeutic agent for the treatment ofdiabetes of the invention will differ depending on the dosage form, butis preferably from 0.00001-100 wt % with respect to the total of thetherapeutic agent for the treatment of diabetes (pharmaceuticalcomposition).

There are no particular restrictions on the dosage form of thetherapeutic agent for the treatment of diabetes according to theinvention, and as examples of oral forms there may be mentionedgranules, powders, tablets, capsules, syrups, emulsions, suspensions andthe like, while as examples of parenteral forms there may be mentionedinjections such as subcutaneous injections, intravenous injections,intramuscular injections and intraperitoneal injections, percutaneousadministration forms such as ointments, creams and lotions, suppositoryforms such as rectal suppositories and vaginal suppositories, andintranasal administration forms and the like.

The process for producing the therapeutic agent for the treatment ofdiabetes according to the invention employs a biguanide derivativerepresented by general formula (1) above or a salt thereof, to producethe therapeutic agent for the treatment of diabetes (preferably atherapeutic agent for the treatment of diabetes with an effect oflowering blood glucose without substantial increase of blood lactic acidlevels, or therapeutic agent for the treatment of diabetes for bloodglucose elevation-suppressing therapy which does not induce lacticacidosis). There are no particular restrictions on the specific processused, and the formulations comprising a biguanide derivative representedby general formula (1) or a salt thereof may be produced by publiclyknown processes which are commonly used in drug formulation steps.Specifically, such formulations may be obtained by appropriate mixtureof prescribed amounts of the biguanide derivative represented by generalformula (1) or the salt thereof, with the additive components, assuitable for the dosage form of the desired therapeutic agent for thetreatment of diabetes.

The effect of “lowering blood glucose levels without substantialincrease of blood lactic acid levels”, as the preferred effect of thetherapeutic agent for the treatment of diabetes according to theinvention, will now be explained.

In the invention, lowering blood glucose levels without substantialincrease of blood lactic acid levels means that when blood glucosereduction rate and blood lactic acid levels are measured by an oralglucose tolerance test, the dosage of the therapeutic agent for thetreatment of diabetes which exhibits a blood glucose reduction rate of60-80% results in a blood lactic acid level increase rate of preferablyno greater than 35%, more preferably 30%, particularly preferably 25%.For example, when blood glucose reduction rate and blood lactic acidlevels are measured by the aforementioned oral glucose tolerance testfor a typical diabetes patient exhibiting an initial blood lactic acidlevel of 4-33 mg/dL, preferably even administration of the therapeuticagent for the treatment of diabetes at a dose which exhibits a bloodglucose reduction rate of 60-80% does not increase the blood lactic acidlevel above 45 mg/dL. Also, at a dose of the therapeutic agent for thetreatment of diabetes which exhibits a blood glucose reduction rate of40-60%, the blood lactic acid level increase rate is preferably nogreater than 15%, more preferably 10%. For example, when blood glucosereduction rate and blood lactic acid levels are measured by theaforementioned oral glucose tolerance test for a typical diabetespatient exhibiting an initial blood lactic acid level of 4-33 mg/dL,preferably even administration of the therapeutic agent, for thetreatment of diabetes at a dose which exhibits a blood glucose reductionrate of 40-60% does not increase the blood lactic acid level above 38mg/dL.

Measurement of blood glucose reduction rate and blood lactic acid levelsby the aforementioned oral glucose tolerance test may be carried out bya publicly known method, and preferred methods are described below.Specifically, 11- to 17-week-old female mice (C57BLKS/J-m +/+ Lepr<db>(db/db)) are starved for 18-24 hours. A group of five or six mice isused for the test. Blood is sampled from the tail for measurement of theblood glucose levels and blood lactic acid levels before treatment ascontrols. After sampling, the biguanide derivative is dissolved inphosphate-buffered physiological saline at a suitable concentration andsubcutaneously administered at a dose of 5 ml/kg. As controls areprepared mice administered only the solvent. Glucose is thenadministered orally at a dose of 3 g/6 ml/kg at 30 minutes afteradministration of the compound or solvent as an oral glucose tolerancetest. Blood is sampled from the tail for measurement of the bloodglucose levels and the blood lactic acid levels 30 minutes, 1 hour and 2hours after glucose administration. The blood glucose levels aremeasured using a New Blood Sugar Test (Roche Diagnostics) or a GlucoseCII-Test Wako (Wako Pure Chemical Industries, Ltd.). The blood lacticacid levels are measured using an “Asuka Sigma” (Sigma Diagnostics).

The blood glucose reduction rate and the blood lactic acid levelincrease rate are calculated according to the following formulas.Blood glucose reduction rate (%)=[(AUC for blood glucose increase levelof solvent-administered group−AUC for blood glucose increase level ofcompound-administered group)/AUC for blood glucose increase level ofsolvent-administered group]×100

The AUC for blood glucose increase level represents the area of theincrease portion in a graph of the blood glucose level changes afterglucose administration plotted with respect to time, up to 2 hours afterglucose administration, with the glucose level prior to glucoseadministration as the baseline. Specifically, the AUC for the bloodglucose increase level may be calculated by the following formula, whereA=blood glucose level before glucose administration, B=blood glucoselevel 30 minutes after glucose administration, C=blood glucose level 1hour after glucose administration, D=blood glucose level 2 hours afterglucose administration.AUC for blood glucose increaselevel=0.5×((A+B)/2−A)+0.5×((B+C)/2−A)+1×((C+D)/2−A)

The blood lactic acid level increase rate is calculated according to thefollowing formula.Blood lactic acid level increase rate (%)=[(AUC for blood lactic acidlevel of compound-administered group−AUC for blood lactic acid level ofsolvent-administered group)/AUC for blood lactic acid level ofsolvent-administered group]×100

The AUC for blood lactic acid level represents the area in a graph ofthe blood lactic acid level changes after glucose administration plottedwith respect to time, up to 2 hours after glucose administration.Specifically, the AUC for the blood lactic acid level may be calculatedby the following formula, where E=blood lactic acid level before glucoseadministration, F=blood lactic acid level 30 minutes after glucoseadministration, G=blood lactic acid level 1 hour after glucoseadministration, H=blood lactic acid level 2 hours after glucoseadministration.AUC for blood lactic acid level=0.5×(E+F)/2+0.5×(F+G)/2+1×(G+H)/2

The preferred object of administration will be explained.

The therapeutic agent for the treatment of diabetes according to theinvention have the excellent hypoglycemic effect as described above, andit preferably lower blood glucose levels without substantial increase ofblood lactic acid levels. It is therefore useful for treatment tosuppress blood glucose level increase which do not induce lacticacidosis, and are effective for administration to diabetic patients andespecially to diabetic patients who are prone to lactic acidosis.Diabetic patients prone to lactic acidosis include, for example,diabetic patients with lactic acidosis anamnesis, diabetic patients withkidney dysfunction, diabetic patients with liver dysfunction, diabeticpatients with cardiovascular dysfunction, diabetic patients withpulmonary dysfunction, diabetic patients susceptible to hypoxia,diabetic patients consuming excessive alcohol, diabetic patients withgastrointestinal disturbance and elderly diabetic patients.

The therapeutic agent for the treatment of diabetes according to theinvention is particularly effective for diabetic patients who are proneto lactic acidosis as explained above, and are especially suitable foradministration to diabetic patients with kidney dysfunction. Kidneydysfunction includes, specifically, for example chronic renal failure,diabetic nephropathy, glomerular nephritis, immune complex nephritis,acute renal failure, interstitial nephritis, renal sclerosis, renalinfarction, abnormal tubular function, drug-induced nephropathy,agricultural chemical-induced nephropathy, uremia, and the like.

A method of suppressing blood glucose elevation and a method of treatingdiabetes using the biguanide derivative of the invention or the saltthereof will now be explained. The method of suppressing blood glucoseelevation may be a method of administering a biguanide derivativerepresented by general formula (1) or a salt thereof, and preferably itis a method of suppressing blood glucose elevation without substantialincrease of blood lactic acid levels. As a method of treating diabetesthere may be mentioned a method comprising a step of administering aneffective dose of a biguanide derivative represented by general formula(1) or a salt thereof to at least one type of diabetes patient selectedfrom the group consisting of diabetic patients with anamnesis of lacticacidosis, diabetic patients with kidney dysfunction, diabetic patientswith liver dysfunction, diabetic patients with cardiovasculardysfunction, diabetic patients with pulmonary dysfunction, diabeticpatients susceptible to hypoxia, diabetic patients consuming excessivealcohol, diabetic patients with gastrointestinal disturbance and elderlydiabetic patients, and a step of suppressing blood glucose elevation(preferably a step of suppressing blood glucose elevation withoutsubstantial increase of blood lactic acid levels).

The method of administering the therapeutic agent for the treatment ofdiabetes according to the invention is not particularly restricted, andfor example, the agent may be administered orally or parenterally as apharmaceutical composition (preparation) using the aforementionedadditives with a biguanide derivative represented by general formula (1)or its pharmacologically acceptable salt.

The dosage of a biguanide derivative represented by general formula (1)or its salt may be appropriately determined based on the species ofsubject (human or other warm-blooded animal, for example), the severityof symptoms, the age, route of administration, physician diagnosis,etc., and for an adult, for example, the dosage of a biguanidederivative represented by general formula (1) will be preferably0.1-2000 mg/kg per day in the case of oral administration, andpreferably 0.1-1000 mg/kg per day in the case of parenteraladministration. These dosages are the values per unit weight (1 kg) ofthe subject of administration. According to the invention, the dosagemay be administered once during a period of 1-7 days or divided overseveral times, depending on the severity of symptoms, the physiciandiagnosis, etc.

By thus administering an effective dose of a biguanide derivativerepresented by general formula (1) or its salt, it is possible, asdescribed above, to adequately suppress increase in blood glucoselevels, and to sufficiently lower blood glucose levels, preferablyadequately inhibiting increase in blood lactic acid levels.

EXAMPLES

The present invention will now be explained in greater detail throughexamples and comparative examples, with the understanding that theseexamples are not limitative on the invention.

Examples 1-2 and Comparative Examples 1-16 Synthesis Example 1 Synthesisof 1-[(furan-3-yl)methyl]biguanide)

To a solution of (furan-3-yl)methylamine (1.79 g) in 1,2-dichloroethane(13 mL) was added trimethylsilyl trifluoromethanesulfonate (4.00 mL),and the mixture was stirred at room temperature for 30 minutes, and thencyanoguanidine (1.55 g) was added, and the mixture was further stirredat room temperature for 1.5 hours, and heated and stirred for 3 hours inan oil bath at 50° C. The reaction mixture was subjected toamine-treated silica gel column chromatography(methanol:chloroform=10:100) to give the target compound (2.30 g) as anoil. The results of structural analysis of the resultant oil were asfollows.

¹H-NMR (DMSO-d₆) δ: 4.15 (2H, s), 6.47 (1H, brs), 6.40-8.30 (6H, m),7.59 (2H, brs)

MS (ESI⁺): 182 [M+1]⁺

HPLC RT: 6.2 min (mobile phase: 10% methanol)

The structural formula of the obtained compound is shown below.

The amine-treated silica gel chromatography was conducted using a SilicaGel Chromatorex NH DM1020 (10 mm particle size) by Fuji Silysia ChemicalCo., Ltd. The HPLC apparatus was L-6200 by Hitachi, the HPLC column wasDevelosil ODS HG-5, 4.6×150 mm by Nomura Chemical, and measurement ofthe retention time (RT: min) by HPLC was carried out by the followingmethod. Specifically, an aqueous solution of 10% methanol/0.1 M ammoniumacetate was used as the mobile phase, with a flow rate of 1 ml/min anddetection at 240 nm. LCMS was conducted by the ionization method (ESI⁺)using LCQ by Thermo Finigan.

(Oral Glucose Tolerance Test)

Eleven- to seventeen-week-old female mice (C57BLKS/J-m +/+ Lepr<db>(db/db)) were starved for 18-24 hours, and a group of six mice was usedfor the test. Blood was sampled from the tail for measurement of theblood glucose levels and blood lactic acid levels before treatment.After sampling, the compounds listed in Table 1 (Examples 1-2) weredissolved in phosphate-buffered physiological saline to give the dosagesalso listed in Table 1, and were subcutaneously administered to the miceat a dose of 5 ml/kg. For comparison, phenformin in the doses shown inTable 1 (Comparative Examples 1-8) and metformin in the doses shown inTable 1 (Comparative Examples 9-16) was subcutaneously administered tomice similarly. As a control, the solvent alone was subcutaneouslyadministered to mice similarly.

Glucose was then administered orally at a dose of 3 g/6 ml/kg at 30minutes after administration of the compound or solvent as an oralglucose tolerance test. Blood was sampled from the tail for measurementof the blood glucose levels and blood lactic acid levels 30 minutes, 1hour and 2 hours after glucose administration. The blood glucose levelswere measured using a New Blood Sugar Test (Roche Diagnostics) or aGlucose CII-Test Wako (Wako Pure Chemical Industries, Ltd.). The bloodlactic acid levels were measured using an “Asuka Sigma” (SigmaDiagnostics).

The test results (blood glucose reduction rates and blood lactic acidlevel increase rates) are shown in Table 1. TABLE 1 Blood Blood lacticglucose acid level Dosage reduction increase Compound (mg/kg) rate (%)rate (%) Ex.1 1-[(Furan-3- 50 40.3 — yl)methyl] biguanide Ex. 21-[(Furan-3- 75 65.5 9.7 yl)methyl] biguanide Comp. Ex. 1 Phenformin37.5 39.5 46.4 Comp. Ex. 2 Phenformin 37.5 72.7 83.1 Comp. Ex. 3Phenformin 75 64.5 93.6 Comp. Ex. 4 Phenformin 75 78.0 151.6 Comp. Ex. 5Phenformin 75 60.8 94.7 Comp. Ex. 6 Phenformin 75 61.4 120.8 Comp. Ex. 7Phenformin 75 72.8 141.1 Comp. Ex. 8 Phenformin 75 69.6 114.8 Comp. Ex.9 Metformin 100 29.1 4.1 Comp. Ex. 10 Metformin 100 12.9 3.7 Comp. Ex.11 Metformin 150 32.5 25.8 Comp. Ex. 12 Metformin 150 24.0 10.7 Comp.Ex. 13 Metformin 150 19.6 20.2 Comp. Ex. 14 Metformin 150 48.3 16.5Comp. Ex. 15 Metformin 200 56.0 36.0 Comp. Ex. 16 Metformin 200 41.861.5

Consequently, administration of a biguanide derivative of the inventionrepresented by general formula (1) above or its salt was confirmed toextremely minimize increase in blood lactic acid levels while exhibitinga notable hypoglycemic effect.

Industrial Applicability

As explained above, the biguanide derivative of the invention and thesalt thereof can be used to provide a therapeutic agent for thetreatment of diabetes which adequately suppress blood glucose levelelevation and even adequately lower blood glucose levels, and preferablydo so while adequately inhibiting blood lactic acid level elevation. Theinvention can therefore satisfactorily suppress blood glucose levelelevation while avoiding blood lactic acid level increase, and therebyprovides an agent for prevention or treatment of hyperglycemia that alsoprevent lactic acid acidosis, for diabetic patients who are susceptibleto lactic acidosis.

1. A biguanide derivative represented by the following general formula(1) or a salt thereof:

(wherein R¹, R² and R³ may be the same or different and each representsone selected from the group consisting of hydrogen, an optionallysubstituted lower alkyl group and an optionally substituted loweralkylthio group):
 2. A therapeutic agent for the treatment of diabetes,comprising as an active ingredient a biguanide derivative represented bythe following general formula (1) or a salt thereof:

(wherein R¹, R² and R³ may be the same or different and each representsone selected from the group consisting of hydrogen, an optionallysubstituted lower alkyl group and an optionally substituted loweralkylthio group).
 3. The therapeutic agent for the treatment of diabetesaccording to claim 2, which has an effect of lowering blood glucoselevels without a substantial increase of blood lactic acid levels. 4.The therapeutic agent for the treatment of diabetes according to claim 2or 3, wherein the target disease is at least one disease selected fromthe group consisting of diabetes with anamnesis of lactic acidosis,diabetes with kidney dysfunction, diabetes with liver dysfunction,diabetes with cardiovascular dysfunction, diabetes with pulmonarydysfunction, hypoxia-susceptible diabetes, diabetes with excessivealcohol consumption, diabetes with gastrointestinal disturbance andelderly diabetes.
 5. The therapeutic agent for the treatment of diabetesaccording to claim 4, wherein the target disease is diabetes with kidneydysfunction.
 6. The therapeutic agent for the treatment of diabetesaccording to claim 2, which is used for the suppression of blood glucoseelevation without inducing lactic acidosis.